In recent years, a technique of increasing the recording density of a magnetic disk has been developed for a magnetic disk apparatus. Data to be recorded on the magnetic disk is encoded by an encoding algorithm having an error correcting capability.
Furthermore, as the density of the magnetic disk increases recently and/or the like, the necessity of considering the influence of noise included in a signal to be read by the read head of the magnetic disk apparatus is growing.
For example, because of the increase in the recording density of the magnetic disk, the degradation of the read head positioning accuracy, and the decrease in the width of a write head, the read head sometimes reads noise from an adjacent data track.
Even in one track, the S/N ratio may vary between the data sectors. A mismatch may occur between the optimization parameters of the read channel of the magnetic disk adjusted for each of data sectors and the optimization parameters to be applied to the data sector under the read. That is, adjustment is necessary for preventing, with real time, the variation of the S/N ratio for the data sector under the read from affecting the optimization parameters.